Bug 13417: Remove warnings

Bug 13417: Remove warnings

Without this patch
  perl -wc C4/VirtualShelves.pm
failed:
Constant subroutine C4::VirtualShelves::SHELVES_MASTHEAD_MAX redefined
at /usr/share/perl/5.20/constant.pm line 156.
Constant subroutine C4::VirtualShelves::SHELVES_COMBO_MAX redefined at
/usr/share/perl/5.20/constant.pm line 156.
Constant subroutine C4::VirtualShelves::SHELVES_MGRPAGE_MAX redefined at
/usr/share/perl/5.20/constant.pm line 156.
Constant subroutine C4::VirtualShelves::SHELVES_POPUP_MAX redefined at
/usr/share/perl/5.20/constant.pm line 156.
Constant subroutine C4::VirtualShelves::SHARE_INVITATION_EXPIRY_DAYS
redefined at /usr/share/perl/5.20/constant.pm line 156.
Subroutine GetShelves redefined at C4/VirtualShelves.pm line 103.
Subroutine GetAllShelves redefined at C4/VirtualShelves.pm line 159.
Subroutine GetSomeShelfNames redefined at C4/VirtualShelves.pm line 189.
Subroutine GetShelf redefined at C4/VirtualShelves.pm line 230.
Subroutine GetShelfContents redefined at C4/VirtualShelves.pm line 262.
Subroutine AddShelf redefined at C4/VirtualShelves.pm line 315.
Subroutine AddToShelf redefined at C4/VirtualShelves.pm line 353.
Subroutine ModShelf redefined at C4/VirtualShelves.pm line 394.
Subroutine ShelfPossibleAction redefined at C4/VirtualShelves.pm line
454.
Subroutine DelFromShelf redefined at C4/VirtualShelves.pm line 545.
Subroutine DelShelf redefined at C4/VirtualShelves.pm line 589.
Subroutine GetBibliosShelves redefined at C4/VirtualShelves.pm line 603.
Subroutine ShelvesMax redefined at C4/VirtualShelves.pm line 628.
Subroutine HandleDelBorrower redefined at C4/VirtualShelves.pm line 648.
Subroutine AddShare redefined at C4/VirtualShelves.pm line 683.
Subroutine AcceptShare redefined at C4/VirtualShelves.pm line 703.
Subroutine IsSharedList redefined at C4/VirtualShelves.pm line 731.
Subroutine RemoveShare redefined at C4/VirtualShelves.pm line 750.
Subroutine _shelf_count redefined at C4/VirtualShelves.pm line 764.
Subroutine _CheckShelfName redefined at C4/VirtualShelves.pm line 788.
C4/VirtualShelves.pm syntax OK

Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>